#重构--在大型项目中，经常需要在添加新代码前重构既有代码
import sys
from time import sleep
import pygame
from bullet import Bullet
from alien import Alien

def fire_bullet(ai_settings, screen, ship, bullets):
	"""若还未达到限制，则发射子弹"""
	# 创建一颗子弹，并将其加入到编组bullets中
	if len(bullets) < ai_settings.bullets_allowed:
		new_bullet = Bullet(ai_settings, screen, ship)
		bullets.add(new_bullet)
		
		
def check_keydown_events(event, ai_settings, screen, ship, bullets):
	"""响应按键"""
	if event.key == pygame.K_RIGHT:
		ship.moving_right = True
	elif event.key == pygame.K_LEFT:
		ship.moving_left = True
	elif event.key == pygame.K_SPACE:
		fire_bullet(ai_settings, screen, ship, bullets)
	elif event.key == pygame.K_q:
		sys.exit()
		

def check_keyup_events(event, ship):
	"""响应松开"""
	if event.key == pygame.K_RIGHT:
		ship.moving_right = False
	elif event.key == pygame.K_LEFT:
		ship.moving_left = False


def check_events(ai_settings, screen, stats, play_button, 
	ship, aliens, bullets):
	"""响应按键和鼠标事件"""
	for event in pygame.event.get():
		if event.type == pygame.QUIT:
			sys.exit()
		elif event.type == pygame.KEYDOWN:
			check_keydown_events(event, ai_settings, 
				screen, ship, bullets)
		elif event.type == pygame.KEYUP:
			check_keyup_events(event, ship)
		elif event.type == pygame.MOUSEBUTTONDOWN:
			mouse_x, mouse_y = pygame.mouse.get_pos()
			check_play_button(ai_settings, screen, stats, play_button, 
				ship, aliens, bullets, mouse_x, mouse_y)
	
			
def check_play_button(ai_settings, screen, stats, play_button, 
	ship, aliens, bullets, mouse_x, mouse_y):
	"""在玩家单击Play按钮时开始新游戏"""
	button_clicked = play_button.rect.collidepoint(mouse_x, mouse_y)
	if button_clicked and not stats.game_active:
		# 重置游戏设置
		ai_settings.initialize_dynamic_settings()
		
		# 隐藏光标
		pygame.mouse.set_visible(False)
		
		# 重置游戏统计信息
		stats.reset_stats()
		stats.game_active = True

		# 清空外星人列表和子弹列表
		aliens.empty()
		bullets.empty()
		
		# 创建一群新的外星人，并让飞船居中
		creat_fleet(ai_settings, screen, ship, aliens)
		ship.center_ship()
		
		
def update_screen(ai_settings, screen, stats, sb, ship, 
	alien, bullets, play_button):
	"""更新屏幕上的图像，并切换到新屏幕"""
	# 每次循环都重绘屏幕
	screen.fill(ai_settings.bg_color)
	# 在飞船和外星人后面重绘所有子弹(对编组调用draw会自动根据rect画位置)
	for bullet in bullets.sprites():
		bullet.draw_bullet()
	ship.blitme()
	alien.draw(screen)
	#显示得分
	sb.show_score()
	
	# 如果游戏处于非活动状态，就绘制Play按钮
	if not stats.game_active:
		play_button.draw_button()
		
	# 让最近绘制的屏幕可见
	pygame.display.flip()


def update_bullets(ai_settings, screen, stats, sb, ship, aliens, bullets):
	"""更新子弹位置，删除消失子弹"""
	# 更新子弹位置
	bullets.update()		
	# 删除已消失的子弹
	for bullet in bullets.copy():
		if bullet.rect.bottom <= 0:
			bullets.remove(bullet)
	# 检查是否有子弹击中了外星人，若有，删除相应子弹和外星人	
	check_bullet_alien_collisions(ai_settings, screen, stats, sb, 
		ship, aliens, bullets)


def check_bullet_alien_collisions(ai_settings, screen, stats, sb, 
	ship, aliens, bullets):
	"""响应子弹和外星人的碰撞"""
	collisions = pygame.sprite.groupcollide(bullets, aliens, True, True)
	
	if collisions:
		for aliens in collisions.values():
			stats.score += ai_settings.alien_points * len(aliens)
			sb.prep_score()
		
	if len(aliens) == 0:
		# 删除现有的子弹并新建一群外星人, 加快游戏节奏
		bullets.empty()
		ai_settings.increase_speed()
		creat_fleet(ai_settings, screen, ship, aliens)
	
	
def get_number_aliens_x(ai_settings, alien_width):
	"""计算每行可容纳多少个外星人"""
	available_space_x = ai_settings.screen_width - 2 * alien_width
	number_aliens_x = int(available_space_x / (2 * alien_width))
	return number_aliens_x
		
		
def get_number_rows(ai_settings, ship_height, alien_height):
	available_space_y = (ai_settings.screen_height - 
		ship_height - 3 * alien_height)
	number_rows = int(available_space_y	 / (2 * alien_height))
	return number_rows
	
	
def creat_alien(ai_settings, screen, aliens, alien_number, row_number):
	"""创建一个外星人并放在当前行"""
	alien = Alien(ai_settings, screen)
	alien_width = alien.rect.width
	alien.x = (alien_width + 2 * alien_width * alien_number)
	alien.rect.x = alien.x
	alien.rect.y = (alien.rect.height +
		2 * alien.rect.height * row_number)
	aliens.add(alien)


def creat_fleet(ai_settings, screen, ship, aliens):
	"""创建外形人群"""
	#外星人间距为外星人宽度
	alien = Alien(ai_settings, screen)
	number_aliens_x = get_number_aliens_x(ai_settings, alien.rect.width)
	number_rows = get_number_rows(ai_settings, ship.rect.height, 
		alien.rect.height)
		
	#创建外星人
	for row_number in range(number_rows):		
		for alien_number in range(number_aliens_x):
			creat_alien(ai_settings, screen, aliens, 
				alien_number, row_number)


def check_fleet_edges(ai_settings, aliens):
	"""有外星人到达边缘时，采取措施"""
	for alien in aliens.sprites():
		if alien.check_edges():
			change_fleet_direction(ai_settings, aliens)
			break
			
	
def change_fleet_direction(ai_settings, aliens):
	"""将整群外星人下移并改变方向"""
	for alien in aliens.sprites():
		alien.rect.y += ai_settings.fleet_drop_speed
	ai_settings.fleet_direction *= -1
	
	
def ship_hit(ai_settings, stats, screen, ship, aliens, bullets):
	"""响应被外星人撞到的飞船，或外星人到达底部"""
	if stats.ships_left > 0:
		# 将ships_left减1
		stats.ships_left -= 1
		print(stats.ships_left)
		# 清空外星人列表和子弹列表
		aliens.empty()
		bullets.empty()
		
		# 重新创建飞船和外星人
		creat_fleet(ai_settings, screen, ship, aliens)
		ship.center_ship()
		
		#暂停一会儿
		sleep(0.5)
	else:
		stats.game_active = False
		pygame.mouse.set_visible(True)

def check_aliens_bottom(ai_settings, stats, screen, ship, aliens, bullets):
	"""检查是否有外星人到达顶端, 若有，调用ship_hit"""
	screen_rect = screen.get_rect()
	for alien in aliens.sprites():
		if alien.rect.bottom >= screen_rect.bottom:
			ship_hit(ai_settings, stats, screen, ship, aliens, bullets)
			break
	
	
def update_aliens(ai_settings, stats, screen, ship, aliens, bullets):
	"""更新外星人位置"""
	check_fleet_edges(ai_settings,aliens)
	aliens.update()
	
	# 检测外星人和飞船之间的碰撞
	if pygame.sprite.spritecollideany(ship, aliens):
		ship_hit(ai_settings, stats, screen, ship, aliens, bullets)
	# 检查是否有外星人到达底端
	check_aliens_bottom(ai_settings, stats, screen, ship, aliens, bullets)
